U.S. patent application number 12/264294 was filed with the patent office on 2009-05-07 for digital data reproducing device.
Invention is credited to Masaru SUGANO, Koichi TAKAGI, Yousuke TOYOTA.
Application Number | 20090119781 12/264294 |
Document ID | / |
Family ID | 40589523 |
Filed Date | 2009-05-07 |
United States Patent
Application |
20090119781 |
Kind Code |
A1 |
SUGANO; Masaru ; et
al. |
May 7, 2009 |
DIGITAL DATA REPRODUCING DEVICE
Abstract
The present invention provides a digital data reproducing device
having a simple configuration and being capable of protecting
copyright of digital data such as video or audio. Content provider
side embeds copyright management information (cumulative number of
reproduction times, permissible number of reproduction times, etc.)
into digital data that has been degraded by scrambling, and
provides it to a content user. A reproducing device of the content
user side causes copyright management information detection unit to
detect the copyright management information, decreases the data
degradation depending on result of the detection, and reproduces by
data reproducing unit.
Inventors: |
SUGANO; Masaru; (Saitama,
JP) ; TAKAGI; Koichi; (Saitama, JP) ; TOYOTA;
Yousuke; (Saitama, JP) |
Correspondence
Address: |
WESTMAN CHAMPLIN & KELLY, P.A.
SUITE 1400, 900 SECOND AVENUE SOUTH
MINNEAPOLIS
MN
55402
US
|
Family ID: |
40589523 |
Appl. No.: |
12/264294 |
Filed: |
November 4, 2008 |
Current U.S.
Class: |
726/26 ;
380/200 |
Current CPC
Class: |
H04N 21/4405 20130101;
H04N 21/8355 20130101; H04N 21/440254 20130101; G06Q 2220/12
20130101; G06F 21/10 20130101; H04N 7/163 20130101; H04N 21/4627
20130101 |
Class at
Publication: |
726/26 ;
380/200 |
International
Class: |
G06F 21/00 20060101
G06F021/00; H04N 7/171 20060101 H04N007/171 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 5, 2007 |
JP |
2007-287447 |
Claims
1. A reproducing device of digital data such as video or audio, the
digital data reproducing device, comprising: data reading unit for
reading digital data that has been degraded in advance (hereinafter
referred to as degraded data); copyright management information
detection unit for detecting copyright management information
embedded in the degraded data; data degradation decreasing unit for
decreasing degradation of the degraded data based on the copyright
management information; and data reproducing unit for reproducing
the degraded data where the degradation has been decreased
(hereinafter referred to as data with decreased degradation).
2. The digital data reproducing device according to claim 1,
further comprising: copyright management information updating unit
for updating the copyright management information; copyright
management information embedding unit for embedding the updated
copyright management information into the degraded data again; and
data storing unit for writing into an storage medium the degraded
data where the copyright management information has been
updated.
3. The digital data reproducing device according to claim 1,
wherein: the degraded data is scrambled digital data, and the data
degradation decreasing unit descrambles.
4. The digital data reproducing device according to claim 3,
wherein: the scrambling is multilayered by at least any of
scrambling intensity, an area to which the scrambling is applied,
and time length during which the scrambling is applied, and the
data degradation decreasing unit descrambles according to copyright
management information detected by the copyright management
information detection unit, by removing in stages the scrambling
intensity, the scrambling area, and the scrambling time length,
respectively.
5. The digital data reproducing device according to claim 4,
wherein: the data degradation decreasing unit completely
descrambles before the copyright management information is updated,
and reduces level of descrambling as the copyright management
information is updated.
6. The digital data reproducing device according to claim 4,
wherein: the data degradation decreasing unit does not descrambles
before the copyright management information is updated, and
increases the level of descrambling as the copyright management
information is updated.
7. The digital data reproducing device according to claim 1,
wherein: the degraded data includes key information showing content
of the process of scrambling; and the data degradation decreasing
unit descrambles by using the key information and the copyright
management information.
8. The digital data reproducing device according to claim 2,
wherein: the copyright management information is embedded in the
degraded data by digital watermark; the copyright management
information detection unit detects the copyright management
information embedded by the digital watermark; the copyright
management information updating unit updates the copyright
management information; and the copyright management information
embedding unit embeds the updated copyright management information
into the degraded data again as the digital watermark.
9. The digital data reproducing device according to claim 8,
wherein: the copyright management information is cumulative number
of reproduction times representing number of times that the
degraded data has been reproduced; and the copyright management
information updating unit increases the cumulative number of
reproduction times as the degraded data is reproduced.
10. The digital data reproducing device according to claim 9,
wherein: permissible number of reproduction times is further
embedded as the copyright management information, the cumulative
number of reproduction times and the permissible number of
reproduction times of the degraded data are compared, and the
degradation is decreased, when the cumulative number of
reproduction times is below the permissible number of reproduction
times.
11. The digital data reproducing device according to claim 8,
wherein: the copyright management information is time elapsed since
a first reproduction of the degraded data or time elapsed since
purchasing; and the copyright management information updating unit
increases the time elapsed since a first reproduction or the time
elapsed since purchasing, as the degraded data is reproduced.
12. The digital data reproducing device according to claim 11,
wherein: a time limit for use of the degraded data is further
embedded as the copyright management information, the elapsed time
and the time limit for use of the degraded data are compared, and
the degradation is decreased when the elapsed time is below the
time limit for use.
13. The digital data reproducing device according to claim 9,
wherein: the copyright management information further includes an
identifier of a digital data reproducing device of a user who
obtains digital data; the copyright management information
detection unit further includes unit for comparing the identifier
included in the copyright management information with the
identifier of a current reproducing device; and only when both
match, the data degradation decreasing unit is applied, and when
both do not match, the data degradation decreasing unit is skipped
or the level of decreasing the degradation is reduced.
14. The digital data reproducing device according to claim 13,
wherein: when the both do not match, the data degradation
decreasing unit reduces the level of decreasing the degradation as
a result of adding any number to the cumulative number of
reproduction times or multiplying the cumulative number of
reproduction times by any number.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a digital data reproducing
device, and more specifically, a digital data reproducing device
that is capable of controlling degradation level of digital data
according to number of reproduction times, a time limit for
reproduction, or copy operation, and of contributing to copyright
protection, in reproducing devices for reproducing digital data
such as video, audio in particular.
[0003] 2. Description of the Related Art
[0004] Japanese Patent Application Laid-Open (JP-A) No. 2006-279428
(Patent Document 1) discloses a compressed data scrambling delivery
device with means for applying a plurality of scrambles to encoded
data, and embedding into scrambled compressed data a signal for
discriminating the applied scrambled signals as digital watermark
data. When reproducing the data, the device determines a method of
descrambling based on the embedded signals as the digital
watermark, and descrambles the compressed data using the
method.
[0005] JP-A No. 2004-030630 (Patent Document 2) discloses a method
of a content provider specifying a quality degradation policy or a
quality degradation specification model for every digital data,
wherein if the digital data is copied or moved, the copied data
will be degraded according to the policy or the model.
[0006] JP-A No. 2001-067794 (Patent Document 3) discloses means for
holding in a header of content data a reproducible period, number
of reproducible times, and number of reproduction times, and for
determining whether or not to reproduce depending on the
reproducible period or the number of reproducible times.
[0007] JP-A No. 2002-006885 (Patent Document 4) rewrites content of
digital data based on condition information showing a time limit
for reproduction when the time limit for reproduction reaches, and
notifies that the time limit for reproduction is approaching, by
doing this rewrite whenever reproduction is performed.
[0008] JP-A No. 2006-127656 (Patent Document 5) discloses means for
mixing noise into content data limited in number of reproduction
times, as the number of reproduction times approaches the limited
number of reproduction times, and for causing the data to degrade
in stages.
[0009] In an approach of the Patent Document 1, as it is necessary
to have a key corresponding to each scramble when a plurality of
scrambles are applied to single digital data, amount of data to be
embedded as digital watermark increases, thereby possibly degrading
quality of digital data.
[0010] In an approach of the Patent Document 2, as it is necessary
to specify a quality degradation policy for every digital data,
operation cost involved in delivery of content of a content
provider will be enormous. Furthermore, the approach does not
disclose a method of degradation associated with number of
reproduction times of digital data.
[0011] By contrast, although the Patent Documents 3, 4, and 5
disclose a mechanism of degrading data as number of reproduction
times increases, based on the number of reproduction times and
information related thereto, data itself flows normally in any
case. Thus, if any normal reproducing device other than those
disclosed in these Patent Documents is used, there is a problem
that desired operation cannot be achieved because information of
number of reproduction times cannot be interpreted.
[0012] In addition, in all of prior arts, it is not assumed to
gradually refine degraded digital data according to the information
on the number of reproduction times.
SUMMARY OF THE INVENTION
[0013] It is an object of the present invention to provide a
digital data reproducing device having a simple configuration and
being capable of protecting copyright of digital data such as video
or audio.
[0014] In order to achieve the object, the present invention has a
characteristic that a reproducing device of digital data such as
video or audio, the digital data reproducing device comprises data
reading unit for reading digital data that has been degraded in
advance, copyright management information detection unit for
detecting copyright management information embedded in the degraded
data, data degradation decreasing unit for decreasing degradation
of the degraded data based on the copyright management information,
and data reproducing unit for reproducing the degraded data where
the degradation has been decreased.
[0015] The present invention has another characteristic that the
copyright management information is embedded in the degraded data
by digital watermark, the copyright management information
detection unit detects the copyright management information
embedded by the digital watermark, and the copyright management
information updating unit updates the copyright management
information and embeds the updated copyright management information
into the degraded data again as the digital watermark.
[0016] In addition, the present invention has another
characteristic that it degrades in advance digital data to be
distributed, thereby controlling level of decreasing the
degradation by number of reproduction times, a time limit for
reproduction, or whether or not there is a copy.
[0017] According to the present invention, as degradation level of
such digital data as video or audio, being distributed in degraded
condition can be controlled according to number of reproduction
times, elapsed time, or copy operation, copyright of the digital
data can be protected.
[0018] In addition, as digital data to be delivered is data in
degraded condition, only degraded data is reproduced if it is
reproduced by a normal reproducing device that has no reproducing
function of the present invention. Therefore, copyright of the
digital data can be protected.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a block diagram showing a schematic configuration
of a first embodiment of the present invention.
[0020] FIG. 2 is a drawing showing three aspects of decrease of
degradation.
[0021] FIG. 3 is a block diagram showing a schematic configuration
of a second embodiment of the present invention.
[0022] FIG. 4 is a flowchart showing how to count number of
reproduction times.
[0023] FIG. 5 is a block diagram showing a schematic configuration
of a third embodiment of the present invention.
[0024] FIG. 6 is a block diagram showing a schematic configuration
of a fourth embodiment of the present invention.
[0025] FIG. 7 is a block diagram showing outline of operations of
content provider side.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0026] The present invention will be described hereinafter with
reference to the accompanying drawings. Although the description
covers video data encoded in an MPEG format, the present invention
can be applied to any media data such as audio data as well as
video data. In addition, media data may be in any compression
format or may be uncompressed.
[0027] In addition, it is assumed that unit for degrading data
shall apply reversible degradation to target video data in advance.
Although degradation level can be set optionally, a structure
(syntax) as video data should be held. Thus, a normal video
reproducing device can reproduce degraded video data without
causing an error. A scrambling scheme can be used as unit for
degrading data, and a technology disclosed in JP-A No. 2007-174375
can be used as multilayered scrambling to video data encoded in an
MPEG format, for example. By dividing the process of adding any
scramble value to DC components in a DCT coefficient block in
multiple times, the intensity of scrambling can be changed in
stages according to the number of the processed blocks.
[0028] With reference to FIG. 7, the function of content provider
side that is a prerequisite for the present invention will be
briefly described. The content provider side applies scrambling
(reversible degradation) to video data encoded in an MPEG format in
a scrambling unit 21, embeds in the video data copyright management
information to be described later in a digital watermark insertion
unit 22, and transmits or provides it to content user side.
Embedding copyright management information in video data by a
digital watermark is one example, and any other method such as
inserting into a header of video data, for example, may be
used.
[0029] Next, a digital data reproducing device according to a first
embodiment of the present invention will be described with
reference to a block diagram of FIG. 1. In the following, a
description will be given on a video data reproducing device, by
way of example.
[0030] The video data that was provided via a communication medium
or a storage medium by the content provider and reversibly degraded
by the scrambling is read into data reading unit 1. Then, when
operation of reproducing the video data is specified, copyright
management information detection unit 2 detects copyright
management information embedded in the video data. As copyright
management information, cumulative number of reproduction times NP
is used, and the copyright management information embedded in the
video data has a value of "0" in a stage that content is purchased,
for example.
[0031] Next, copyright management information updating unit 3
updates the copyright management information. For example, in the
case of a first (first-time) reproduction, output of the copyright
management information updating unit 3 is "1", and the updated
copyright management information is sent to data degradation
decreasing unit 4 and copyright management information embedding
unit 6. The copyright management information embedding unit 6
embeds the updated copyright management information into the
degraded data again. The degraded data in which the copyright
management information has been updated can be written into a
storage medium, as necessary. In addition, "0" prior to updating
may be used as the copyright management information to be sent to
the data degradation decreasing unit 4.
[0032] The data degradation decreasing unit 4 decreases degradation
of video data based on the output of the copyright management
information updating unit 3, and thus a frame of the video data is
reproduced. The video data where degradation has been decreased is
sent to a data reproducing unit 5 where it is reproduced.
[0033] Now, level of decrease can be set variously, as shown in
FIG. 2. In other words, a method that completely removes
degradation up to P times (P is an integer of P>1) of
reproductions as shown in FIG. 2(a), a method that completely
removes degradation up to P1 time of reproduction and decreases
removal of degradation in a discrete (nonlinear) manner as
reproduction proceeds P2 times, P3 times, P4 times, as shown in
FIG. 2(b), and a method that decreases removal of degradation in a
continuous (linear) manner as the number of reproduction times
increases, as shown in FIG. 2(c) can be set.
[0034] Use of multilayered scrambling enables control of
degradation according to copyright management information, by
descrambling in stages with a value of the copyright management
information as a parameter. First, an example of decreasing the
intensity of scrambling in stages will be described. For example,
if scrambling for shifting DCT coefficient blocks in a macro block
was applied, the process of returning all shifted blocks to their
original positions when a value of the copyright management
information is "1" and of decreasing the number of blocks to be
returned to their original positions, as the value of the copyright
management information increases by predetermined number of times
may be performed. Alternatively, types of scrambling applied may be
held as separate key information. In this case, it can be
determined in the video reproducing device based on the key
information and the copyright management information how much
target scrambling is to be decreased. The key information may be
held by a method of embedding it as a file independent of video
data, a header of video data, or a digital watermark. If the key
exists as an independent file, it can be obtained through a
different path as well as the same path.
[0035] As a second example of descrambling in stages, decreasing
removal of areas to which scrambling is applied may be cited. Now,
a frame is divided in advance into some regions, R regions, for
example, to each of which scrambling is applied. The process of
descrambling all of R regions when a value of the copyright
management information is "1", and reducing the number of regions
where descrambling is applied as the value of the copyright
management information increases may be performed. With this,
although the entire frame can be initially viewed without any
degradation, degraded area in the frame will expand as the
cumulative number of reproduction times NP increases.
[0036] As a third example of descrambling in stages, decreasing
length of removal of temporal segments to which scrambling is
applied may be cited. Now, video data is divided in advance into
some temporal segments, S segments, for example, to each of which
scrambling is applied. Then, the process of descrambling all of S
segments when a value of the copyright management information is
"1", and reducing the number of segments where descrambling is
applied as the value of the copyright management information
increases maybe performed. With this, although all segments of the
video data can be initially viewed without any degradation,
degraded temporal segments will increase as the cumulative number
of reproduction times NP increases.
[0037] The processes of descrambling by states as described above
may be used in any combination.
[0038] In addition, in the above examples, the data degradation
decreasing unit completely descrambles before the copyright
management information is updated, and descrambles according to
update of the copyright management information. Contrary to this,
it maybe possible not to descramble before the copyright management
information is updated and to increase scrambling to be removed as
the copyright management information is updated.
[0039] In the following, a second embodiment of the present
invention will be described with reference to FIG. 3. This
embodiment is an example of when non-multilayered scrambling is
used (FIG. 2(a)) wherein control is performed such that no
scrambling is removed when a value of the copyright management
information no longer satisfies a certain condition. Reference
numerals in FIG. 3 that are same as those in FIG. 1 show identical
or equivalent components.
[0040] In this embodiment, as permissible number of reproduction
times and cumulative number of reproduction times are embedded as
copyright management information in degraded video data to be
provided by a content provider, the copyright management
information detection unit 2 detects the permissible number of
reproduction times P and the cumulative number of reproduction
times NP. The cumulative number of reproduction times NP is updated
by the copyright management information updating unit 3, and
compared with the permissible number of reproduction times P by
comparison unit 7. Alternatively, the cumulative number of
reproduction times NP before being updated may be compared with the
permissible number of reproduction times P.
[0041] The comparison result is sent to switching unit 8, and when
P.gtoreq.NP, the switching unit 8 connects degraded data from the
data reading unit 1 to a terminal (a), i.e., the data degradation
decreasing unit 4A, and when P<NP, it connects the degraded data
to a terminal b, i.e., the data reproducing unit 5. Consequently,
when P.gtoreq.NP, degradation of the degraded data is removed by
the data degradation decreasing unit 4A, and data without
degradation is sent to the data reproducing unit 5 and is
reproduced. In contrast, when P<NP, the degraded data is
directly sent to the data reproducing unit 5. Thus, when the
cumulative number of reproduction times exceeds the permissible
number of reproduction times, only the data with degradation is
reproduced.
[0042] The copyright management information updated by the
copyright management information updating unit 3 is sent to the
copyright management information embedding unit 6. The copyright
management information embedding unit 6 embeds the cumulative
number of reproduction times (NP+1) in cumulative management
information into the degraded data from the data reading unit
1.
[0043] As described above, according to this embodiment, when an
permissible number of reproduction times is set as P times and said
condition can no longer be met (i.e., when the cumulative number of
reproduction times NP becomes P+1 time), degraded data is directly
reproduced without descrambling. Then, although the permissible
number of reproduction times P can be directly held by the
reproducing device side (for example, P=20, to all contents), it
can be set for every content by embedding it in the video data as a
part of the copyright management information. If the permissible
number of reproduction times P is embedded in the video data, the
copyright management information updating unit 3 updates the
cumulative number of reproduction times NP only, and does not
update the permissible number of reproduction times P.
[0044] With the above, a reproducing device by which video data
degrades when the video data is reproduced can be configured.
However, in order to implement multilayered degradation in the
reproducing device, not only the copyright management information
is updated but also the updated video data needs to be
overwritten.
[0045] Now, updating of copyright management information when
reproduction ends or is suspended will be described with reference
to a flow chart of FIG. 4. In step S1, digital watermark is
detected, and in Step S2, cumulative number of reproduction times
NP is compared with permissible number of reproduction times P.
When NP<P, the process proceeds to step S3 where the process of
removing degradation is performed, and to step S4 where the
reproduction process is performed. In contrast, when NP>P,
without removal of degradation, the process goes to step S4 where
the reproduction process is performed. The above processes are as
described above.
[0046] When reproduction is suspended, as shown in step S5, e.g.,
if only less than L % of length of video content (L=10) is
reproduced (determination of step S5 is NO), it is not considered
as one reproduction and thus copyright management information is
not updated. In contrast, if L % or more of length of video content
is reproduced (determination of step S5 is YES), it is considered
that one reproduction has been done, and the process proceeds to
step S6 where NP is incremented by 1. Then, the process proceeds to
S7 where the updated copyright management information is embedded
in the video data again and written into the storage medium.
[0047] It is desirable that copyright management information to be
embedded into video data cannot be discovered or extracted only by
interpreting syntax of the data. Thus, the digital watermark
technology can be used as means for detecting and embedding
copyright management information, and, for example, a technology
disclosed as a method of embedding digital watermark in video data
encoded in MPEG in JP-A No. 2006-180034 or a method of updating
(rewriting) digital watermark disclosed in JP-A No. 2007-116513 can
be employed. Alternatively, robustness to attack can be enhanced by
encoding copyright management information before being embedded as
digital watermark.
[0048] According to the operations of the first and second
embodiments, a video data reproducing device can be implemented
that gradually degrades video data according to number of
reproduction times or that completely degrades it when a certain
number of reproduction times is exceeded. In addition, in the
present invention, as video data is distributed in degraded
condition, reproduction operation by any normal reproducing device
other than the reproducing device according to the present
invention reproduces the data in the degraded condition. With this,
even when the video data is obtained illegally, its copyright can
be protected.
[0049] In addition, as the copyright management information is
embedded in video data, a value of the copyright management
information can be taken over if it is copied by a normal copy
manipulation. In other words, in the example described above, if it
is assumed that a value of copyright management information of
video data that has been reproduced 10 times is "10", video data
newly created by copy operation will also have a value of "10" as
copyright management information, and will be updated to "11" when
it is later reproduced once by the video reproducing device
according to the present invention. Hence, even if the video data
is obtained illegally and reproduced by the reproducing device
according to the present invention, a period where an illegal
action is valid can be limited.
[0050] In the following, a third embodiment of the present
invention will be described with reference to FIG. 5. This
embodiment uses number of days elapsed since video content was
purchased as copyright management information. Reference numerals
in FIG. 5 that are same as those in FIG. 1 show identical or
equivalent components.
[0051] When receiving a request for purchase of video content from
a user, the content provider embeds a value of "0" as the copyright
management information and a current date into degraded video data
and delivers it to the consumer.
[0052] Then, a video data reproducing device owned by the consumer
reads the video data into the data reading unit 1, and the
copyright management information detection unit 2 detects number of
elapsed days (t) and a time limit for use (T) that are embedded in
the degraded data. The copyright management information updating
unit 3 updates the number of elapsed days (t) with time information
during reproduction. For example, if video content is purchased on
January 1, the number of elapsed days (t) will be a value of a
combination of "0" and "0101". If a first reproduction is performed
on January 3, the value of the number of elapsed days (t) will be
updated to "2" and "0103". Then, if a second reproduction is
further performed on January 10, the value of the number of elapsed
days (t) will be updated to "9" and "0110". After this, a value of
the number of elapsed days (t) will be incremented according to
date of reproduction. Of the number of elapsed days (t), either of
"0", "2", representing the number of days and the "0101", "0103",
representing date may be omitted.
[0053] The number of elapsed days (t) is sent to the comparison
unit 7. The comparison unit 7 makes a comparison of whether the
number of elapsed days (t) exceeds the time limit for use (T). If
the limit is not passed (t=<T), it connects the switching unit 8
to the terminal (a) side, and if the number of elapsed days (t) is
exceeded (t>T), it connects the switching unit 8 to the terminal
(b) side.
[0054] If the number of elapsed days (t) does not exceed the time
limit for use (T), the data degradation decreasing unit 4 decreases
degradation with the number of elapsed days (t) as a parameter, and
provides the video data after degradation is decreased, to the data
reproducing unit 5. In contrast, if the number of elapsed days (t)
exceeds the time limit for use (T), the video data is sent to the
data reproducing unit 5 without the degraded data being
removed.
[0055] The copyright management information embedding unit 6 embeds
into the degraded data the number of elapsed days (t) that has been
updated by the copyright management information updating unit
3.
[0056] Unlike the first and second embodiments, this embodiment is
characterized in that there is no limit on the number of
reproduction times in one day. In addition, as a variant of this
embodiment, it is possible not to count number of days after
purchase of video content till its first reproduction, as the
number of elapsed days. For example, when video content is
purchased, a value of "-99" that is not considered as the number of
elapsed days, and a date "0101" are embedded as copyright
management information. When a first reproduction is performed, the
value of copyright management information is updated to "0" and
"0103". When a second reproduction is performed, the value of
copyright management information is updated to "7" and "0110". As,
by doing so, the number of days after purchase of video content
till the first reproduction is not counted as the number of elapsed
days, this is an advantageous form for users. For example, if a
video purchaser does not perform a first reproduction immediately
after he/she purchased the video and performs a first reproduction
2 weeks after the purchase, for example, these 2 weeks will not be
considered as the number of elapsed days. Although only the number
of days is now considered as the copyright management information,
number of hours and date of reproduction may be made copyright
management information, by examining date and time during
reproduction. Similar to the operations in the first and second
embodiments, it is possible to implement video data that is
completely degraded after a certain elapsed time is exceeded or
that is gradually degraded according to the elapsed time.
[0057] In addition, in the example described above, although the
copyright management information is expressed as a numeric value,
it can be described as metadata if much amount of information that
can be embedded as digital watermark can be ensured. With this, not
only the cumulative number of reproduction times NP and the
permissible number of reproduction times P but also any information
other than the time limit for reproduction can be embedded. To
describe metadata, an XML format, for example, can be used.
[0058] Next, a fourth embodiment of the present invention will be
described with reference to FIG. 6. Reference numerals in FIG. 6
that are same as those in FIG. 1 show identical or equivalent
components.
[0059] In this embodiment, an identifier of an authorized
reproducing device is embedded as copyright management information,
in addition to the cumulative number of reproduction times NP. In
other words, a field for an identifier of the reproducing device
has been prepared for the copyright management information, and
when video content is purchased, the delivery side embeds the
identifier ePID of the reproducing device of a content purchaser.
As the identifier ePID, an IP address or a MAC address of the
reproducing device can be used.
[0060] In the reproducing device, the copyright management
information detection unit 2 detects the copyright management
information embedded in video data. Then, the comparison unit 7
compares the identifier ePID of the reproducing device contained
therein with the identifier PID of the aforementioned reproducing
device, and the data degradation decreasing unit 4 decreases the
degradation and performs reproduction only when they match. In the
shown example, when the identifiers match, selection unit 9 selects
"0", and the copyright management information updating unit 3 adds
"0" to the cumulative number of reproduction times. As a result, as
the cumulative number of reproduction times does not vary, the data
degradation decreasing unit 4 decreases the degradation.
[0061] In contrast, if the identifiers do not match, the selection
unit 9 selects X (X is an integer greater than 1). Thus, output of
the copyright management information updating unit 3 is (NP+X), and
the data degradation decreasing unit 4 does not decrease the
degradation, or it reduces the level of decrease. After
reproduction, the copyright management information embedding unit 6
updates a variable part of the copyright management information
such as the cumulative number of reproduction times NP, without
updating the identifier ePID of the reproducing device.
[0062] As described above, according to this embodiment, even if a
malicious user copies video content, and attempts to reproduce the
video data with a reproducing device of another user, the
identifier PID of the user's reproducing device and the identifier
ePID of the reproducing device embedded in the video data do not
match, as the identifier ePID of the reproducing device embedded in
the video data is taken over. In addition, in this case, it is
possible either not to decrease degradation or reduce the level of
decrease of degradation, by adding any numeric value X to the
embedded cumulative number of reproduction times NP or multiplying
the embedded cumulative number of reproduction times by any numeric
value X. Thus, in the former case, copying the video data
completely degrades the video data, while in the latter case, the
video data degrades in stages as the video data is copied, which
can thereby avoid infringement of copyright.
[0063] So far the examples in which video data degrades in stages
from its original condition have been described. Contrary to this,
an embodiment for refining video data in stages from the degraded
condition would be possible. In order to refine video data, similar
to the above, the data degradation unit applies in advance
reversible degradation to video data. Then, while a value of the
copyright management information is small or low, the level of
decrease is kept low, and the level of decrease of degradation may
be enhanced as a value of the copyright manager information
increases.
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